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Thursday, 19 April 2012

Is Mammography Screening Always A Good Idea?

I had, like most people, always assumed that mammography screening was a thoroughly good thing. If there was a controversy about, I had assumed it would be one that would come down to costs versus benefits. The assumption being that the only thing stopping mammography screening being rolled out to younger women was just about money. At no point had it ever occured to me that there might be scientific controversies associated with screening. That was until I found out about Peter Gotzsche and his argument that mammography screening was actively harming women. My first thought was that this must be about sloppy diagnosis - if women were being harmed it was because some of them are being misdiagnosed and then subjected to the array of harsh treatments - chemotherapy, radiotherapy and radical surgery. But no, his point is more subtle than that and comes down to basic oncology. His key finding, based on the data from randomised clinical trials, is that women are being over-diagnosed. And it wasn't until I read his book, Mammography Screening: Truth, Lies and Controversy (which I have reviewed here: http://www.londonbookreview.com/lbr0067.html), that I got the point.

In effect it boils down to a simple fact - not all breast cancers will grow, spread and ultimately kill the women who develop them. There are cancers that are slow-growing or which sprout, shrivel and die and which actually do not cause any health problems whatsoever. Many women will develop these types of tumours and never even know it. The problem is that we don't have any clear way of differentiating between these tumours and the ones that turn into killers. What screening does then is pick out all tumours - the safe and the dangerous. And because we don't know which is which doctors have no choice but to treat them all. It's not that women are being misdiagnosed, the tumours that are picked out are real, it's that some of those tumours are less dangerous than the treatments that follow.
Now for women with family histories of breast cancer, carriers of BRCA1 or BRCA2 or who have Li Fraumeni Syndrome or damaged TP53, screening makes sense. But for women, especially young women, with no family history or genetic predisposition, the argument for regular mammography screening is less straightforward. In his book Professor Gotzsche makes the point that many screening programs do not give women all the facts and will tend to make simplistic statements that are often no better than emotional blackmail. Readers are invited to take a look at an alternative screening letter produced by the Nordic Cochrane Centre which attempts to give women all the facts they need to make their own choice on the matter.

And, as an aside, reading Gotzsche's book was an eye-opener in other ways. His description of the controversy and the way that sceptical voices who disagree with the establishment view makes for shocking reading.